The present invention relates to an image forming apparatus and an image forming method. For example, it relates to an image forming apparatus for forming a color image on a piece of recording medium, and an image forming method used with such an image forming apparatus.
A color image forming apparatus is provided with various measures for preventing the apparatus from being used to forge a certain type of original, for example, paper money, securities, and the like. One of such measures is to make it possible to identify the apparatus used for forgery. This can be realized by fixing a color image forming apparatus so that when a copy is produced by the apparatus, a coded pattern, which is specific to the apparatus, and inconspicuous to the naked eye, is overlaid across the copy, with a predetermined interval.
If an image forming apparatus fixed in the above described manner is used to forge securities, the identify of the apparatus used for the forgery, that is, a very effective clue for tracing the forger, can be easily revealed by reading the forgery with the use of a reading apparatus which extracts the code specific to the apparatus. Further, providing an image forming apparatus with such a function is effective to prevent the apparatus from being used for forgery, which is the secondary benefit of such provision.
However, there is a problem in this measure. That is, in the case of an ink jet recording system, the size and shape of a dot formed on a sheet of recording medium by an ink droplet drastically changes depending on the type of recording medium. For example, if an apparatus identification code, or coded pattern, is overlaid with a low density as disclosed in Japanese Laid-Open Patent Application No. 113107/1994, U.S. Pat. No. 5,557,416, or the like, the coded pattern sometimes becomes conspicuous to the naked eye, that is, can be recognized without the use of an apparatus which passes the light in a specific wave length range, and therefore, image quality becomes drastically inferior.
Further, when an image is formed with the use of an ink jet recording system, which is a binary recording system, control can be exercised only at the level of each dot. Therefore, if an apparatus identification pattern is improperly overlaid, image quality is drastically affected. For example, in the case of paper produced specifically for ink jet recording, that is, paper coated with an ink absorption layer, the bleeding which occurs as an ink droplet lands on recording medium is very small, and therefore, a dot with a sharp edge, which is conspicuous to the naked eye, is formed.
On the other hand, when an image is formed on a sheet of ordinary paper, that is, paper which is not coated with the ink absorption layer, ink spreads along the paper fibers as an ink droplet ejected from a recording head lands on the paper, and therefore, a dot with an indistinct edge is formed. Thus, when an image, inclusive of the aforementioned apparatus identification pattern, is formed on a sheet of ordinary paper, it takes a longer time to identify the apparatus with the use of the aforementioned reading instrument which passes only the light with a specific spectrum range, or it is rather difficult to obtain the apparatus identity.
The present invention is made in consideration of the above described shortcomings of the conventional methods. Thus, the object of the present invention is to provide an image forming apparatus capable of recording a predetermined code, in an appropriate size, and a recording method effectively usable with such an image forming apparatus.
Another object of the present invention is to provide an image forming apparatus capable of properly recording a predetermined code regardless of the type of recording medium, and a recording method effectively usable with such an image forming apparatus.
The present invention made for the purpose of accomplishing the above described objects is characterized in that an image forming apparatus for forming an image on a piece of recording medium in response to the image formation signals inputted into the apparatus comprises:
means for generating predetermined patterns;
means for adding to the inputted image formation signals for the primary image, the image formation signals of one of the predetermined patterns generated by said pattern generating means;
means for forming an image, inclusive of the selected predetermined pattern, on a piece of recording medium, in response to the image formation signals compiled by said adding means; and
means for controlling the amount of ink ejected per ejection to form the selected pattern generated by said pattern generating means, in accordance with the type of the recording medium.
Further, the present invention is characterized in that an image forming method for forming an image on a piece of recording medium in response to the image formation signals inputted into the apparatus comprises:
a step for generating predetermined patterns;
a step for adding to the inputted image formation signals for the primary image, the image formation signals of one of the predetermined patterns generated by said pattern generating means;
a step for forming an image, inclusive of the selected predetermined pattern, on a piece of recording medium, in response to the image formation signals compiled by said adding means; and
a step for controlling the amount of ink ejected per ejection to form the selected pattern generated by said pattern generating means, in accordance with the type of the recording medium.
Further, the present invention is characterized in that an image forming apparatus for forming an image on a piece of recording medium in response to the image formation signals inputted into the apparatus comprises:
means for generating predetermined patterns;
means for adding to the inputted image formation signals for the primary image, the image formation signals of one of the predetermined patterns generated by said pattern generating means;
means for forming an image, inclusive of the selected predetermined pattern, on a piece of recording medium, in response to the image formation signals compiled by said adding means; and
means for controlling said image forming means so that the selected predetermined pattern is formed twice or more times across a piece of recording medium, depending upon the type of the recording medium.
Further, the present invention is characterized in that an image forming method for forming an image on a piece of recording medium in response to the image formation signals inputted into the apparatus comprises:
a step for generating predetermined patterns;
a step for adding to the inputted image formation signals for the primary image, the image formation signals of one of the predetermined patterns generated by said pattern generating means; and
a step for forming an image, inclusive of the selected predetermined pattern, on a piece of recording medium, in response to the image formation signals compiled by said adding means;
wherein the selected predetermined pattern is recorded twice or more times across the piece of recording medium, depending upon the type of the recording medium.
According to the above described structure, the amount by which ink is ejected to form the pattern to be overlaid can be altered by controlling the dot matrix, and the dot diameter.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.